For ignition apparatuses, a technique for improving ignitability of an air-fuel mixture in an engine combustion chamber is preferable. As the technique for improving ignitability, there are known a powerful ignition technique for generating strong spark discharge by using a spark plug, and a multiple ignition technique for continuously generating strong spark discharge several times by using a spark plug.
However, these ignition techniques have problems that wear on electrodes of a spark plug increases due to repeated re-discharge, and that power is wastefully consumed. Hence, an ignition apparatus is required which has high ignitability, and which can reduce wear on electrodes of a spark plug and can suppress wasteful power consumption.
As a technique for increasing ignitability and reducing wear on electrodes of a spark plug, a technique for simultaneously activating a “CDI (capacitive discharge) ignition circuit” and a “self-excitation thyristor series inverter ignition circuit” has been proposed (for example, refer to Patent Literature 1).
In the technique of Patent Literature 1, the CDI ignition circuit generates a strong spark discharge multiple times at time intervals, and the self-excitation thyristor series inverter ignition circuit continuously and repeatedly generates a weak spark discharge, whereby “multiple strong spark discharges” and “continuous weak spark discharges” overlap with each other.
(Problem 1)
In the self-excitation thyristor series inverter ignition circuit used in Patent Literature 1, since spark discharges are continued by supplying a current subject to positive and negative resonance to a primary coil, a secondary voltage repeatedly alternates between positive voltage and negative voltage.
As a result, in the technique of Patent Literature 1, due to the alternation of the secondary voltage crossing zero voltage during a spark discharge (during an extension of the spark discharge) by the self-excitation thyristor series inverter ignition circuit, the spark discharge voltage partially lowers in each alternation. As a result, blowout of the spark discharge easily occurs due to a rotational flow or the like generated in a cylinder.
(Problem 2)
The self-excitation thyristor series inverter ignition circuit used in Patent Literature 1 described above uses a complicated resonance circuit (a first resonance circuit using a resonant inductance, a second resonance circuit using a feedback winding, and the like). Hence, the circuit size becomes large. As a result, the ignition apparatus becomes large in size, and increase in cost is caused.